Filament tensioning device



O 9 P. 1. CORBELL ET AL 2,656,480

FILAMENTTENSIONING DEVICE Filed July 9, 1951 4B INV NT R5 E 0 41 40 43 PAUL I. C 01285.

72y? BY ROBERT J. Bu acx &2; w

A TTOIPIVE Y Patented Oct. 20, 1953 FILAMENT TEN SIONIN G DEVICE Paul I. Corbell, Cedar Rapids, and Robert J. Black, Marion, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application July 9, 1951, Serial No. 235,816

. This invention relates in general to filament tensioning devices and in particular to means for maintaining a filament in a predetermined position and shape.

As is Well known to those skilled in the art, it is desirable in electronic tubes to maintain the filaments fixed with respect to other elements. When the filaments are heated, they expand and unless some provision is made for taking up the slack caused by the expansion, distortion and bowing will occur. It has been attempted previously to maintain a filament under tension by attaching a coil or leaf spring to it, but in very high power tubes such arrangements are not satisfactory for the reason that a filament becomes so hot that the spring becomes overheated and loses its flexibility.

It is an object of this invention therefore, to provide a filament which has one end integrally formed into a spring to maintain a filamentv under tension.

Another object of this invention is to provide a filament tensioning device wherein the filament is spring loaded by applying a spring bias to a relatively cool portion of the filament.

Yet another object of the invention is to provide a filament tensioning device which allows thermal expansion of the filament but maintains the filament in a predetermined special relationship.

A feature of this invention is found in the provision of a filament mounted between two fixed members with one end of the filament formed into a coil spring and with a flexible contact engageable with the filament adjacent the coil spring. A heating potential is applied between one supporting means and the flexible contact.

Another feature of this invention is found in the provision of a filament connected between a fixed point and the periphery of a rotatable cam which has a lever arm spring biased so as to tension the filament. A heating potential is applied between the fixed end of the filament and an intermediate point adjacent the cam.

Further objects, features and advantages of this invention will become apparent from the following description and claims when read in view of the drawings, in which;

Figure 1 is a side view of the filament tensioning device of this invention;

Figure 2 is a modification of the filament tensioning device of this invention; and

Figure 3 is a detailed top view of the coil spring of Figure 2.

With reference to Figure 1, a filament H! which 3 Claims. (Cl. 313--278) might be a ribbon of tungsten for example, has its upper end l'l clamped to a supporting means [2 by the screw it and plate is. The lower end it of the filament Iii is connected by a set screw it to the periphery of a cam Iii.

The cam 18 is rotatably supported by a shaft it on a standoff iii, and the standoff 2! is in turn connected to a supporting member 22. The cam i8 is formed with a lever arm 23 which has an opening 24 formed therethrough.

A shaft 26 is connected to member 22 and extends through the opening it. A Washer 21 is mounted over the shaft 26 adjacent the lever arm 23. A coil spring 28 is mounted over the shaft 28 and between the washer 2i and a second Washer 29. A suitable holding means, as for example, a nut 3! is threadedly received on the shaft 255 and the assembly forms a spring bias against the lever arm 23. It is to be noted that the opening 24 is substantially larger than the shaft 26 and thus the lever It may pivot about the shaft IS.

A feed-in conductor 32 is connected to the standoff 2| and is electrically connected to the filament ID by clamping means 33. The clamp 33 comprises clamping plates 3t and 3t and nut and bolt means 31. The lead 32 is flexible so that it will conform to the expansion of the filament I0.

The heating potential is applied between the supporting member l2 and the supporting member 22, and substantially all of the heating current flows through the lead 32 to the supporting means 22. The lead 32 has a relatively low resistance and thus the path from the filament is to the supporting member 22 will have less resistance than the path through the remainder of the filament l6 and the cam 18.

This allows the lower end Id of the filament to remain relatively cool and, thus the tensioning apparatus comprising the earn it and spring 28 are not subjected to excessive temperatures. The spring holds the filament under tension and thus no sagging or bowing is allowed.

Figure 2 illustrates a modification of the invention. The filament it has its upper end H clamped to supporting member l2 and the lower end I6 is integrally formed into a coil spring ts.

The spring 40 is rigidly fastened to a shaft 45 which is mounted to a standoff 42. The shaft M is non-rotatably mounted in the standofi s2 and the tension of the spring 40 is maintained so as to hold the filament I 0 in tension. The standoff 42 is attached to an extension 43 of the member 22 and as best seen in Figure 3, a slot 45 is formed in the extension 43 to receive the spring therein.

Adjacent the lower end It, a clamping means 46 is attached to the filament H3. The clamping means comprises the clamping plates 41 and 48 which are held to the filament by a set screw 50. The clamping plate 48 is connected to a pair of flexible members 49 and 5|, respectively, which have their opposite ends connected to a projection 52 of the member 22.

A heating potential is connected between the members I2 and 22 and the current flows through the filament l and through the members 49 and to the member 22. The members 49 and -51 are made of low resistance material and, thus substantially all of the curreh't'fiows'to the member 22 through them. The spring 40 receives very little current due to the higher re'sistance of the filament.

As expansion of the filament l0 occurs, due to an increasing temperature, the spring 40 takes up the slack and the flexible members 49 and 5| deflect to maintain the filament under tension. The filament will be maintained sub stantially fixed relative to the members [2 and 22 and there will be no bowing.

It is seen that this invention relates to filament tensioning means and although it ha been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

We claim:

1. Means for maintaining a filament under substantially constant tension between a pair of supporting means comprising, first clamping means connecting one end of the filament to one of the supporting means, a standoff attached to the other supporting means, a shaft supported by said standoff, a cam supported on said-shaft, the other end of said filament attached to the periphery of said cam, a lever attached to said cam and extending therefrom, a second shaft extending from the othersupporti-ng means and passing through an opening formed in said lever, spring biasing means attached to said second shaft-and urging said lever arm toward the other supporting means, and a fiexible-feed-in conductor connecting the other supporting means to the filament adjacent the cam.

2. Means for maintaining a filament under tension and in a predetermined special relationship between a pair of supporting members comprising, first clamping means connecting one end of the filament to one of the supporting members, a cam rotatably supported by the other supporting member, the other end of said filament attached to "the periphery of said earn, a lever connected to said cam and extending therefrom, a shaft attached to the other supporting member and passing through an opening formed in said lever, holding means attached to the end of said shaft, a coil spring mounted between the holding means 'andthe lever to spring bias the lever to- Wardthe other supporting member, and a feed-in conductor with one end connected to said filament adjacent the cam and with the other end connected to the other supporting member to provide a low resistance path for current flowing through the filament.

3. Apparatus for tensioning a filament and maintaining it in a predetermined special relationship with respect to a pair of supporting members comprising, a standofi mounted to one or" the supporting members, a shaft attached to said standoif, a substantially circular cam rotata bly supported on said shaft, a lever arm attached to said cam and extending therefrom, a second shaft attached to the one supporting memberahd passing through an-opening formed in said lever arm, said opening substantially larger than the shaft, a holding means attached to the end of said second shaft, a pair of Washers mounted on said second'shaft between the lever arm and the holding means, a spring mounted between said washers, one end of said filament attached to the periphery of said cam, the other end of said filament attached to the other supporting member, and a fiexible feed-in conductor attached to the one supporting member and the filament adjacent the cam.

PAUL I. CORBELL.

ROBERT J. BLACK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,380,502 Clark et a1. July 31, 1945 2,544,664 Gamer et al. Mar. 13, 1951 

